Device having an active channel region

ABSTRACT

In some examples, a transistor includes a drain, a channel, and a gate. The channel surrounds the drain and has a channel length to width ratio. The gate is over the channel to provide an active channel region that has an active channel region length to width ratio that is greater than the channel length to width ratio.

CROSS REFERENCE TO RELATED APPLICATIONS

This is a continuation of U.S. Application No. 15/369,951, filed Dec. 6,2016, which is a continuation of U.S. application Ser. No. 14/112,627,filed Oct. 18, 2013, which is a national stage application under 35U.S.C. §371 of PCT/US2011/037202, filed May 19, 2011, which are allhereby incorporated by reference in their entirety.

BACKGROUND

Integrated circuits include analog and digital circuits made up ofcircuit components, such as transistors, diodes, and resistors.Sometimes, the function of one component is provided by anothercomponent, such as when transistors are configured to provide thefunction of a diode or a resistor.

In some logic circuits, referred to as ratioed logic circuits, resistorsare connected as loads to transistors. In a ratioed logic circuitinverter, a resistive pull-up is connected to a transistor pull-down.The resistance value of the resistive pull-up is chosen to provide a lowoutput voltage in one logic state and to charge the output to a highoutput voltage in the other logic state. A higher resistance valueprovides a lower output voltage and reduces power consumption.

In some semiconductor processes, providing a resistor with a higherresistance value consumes a large amount of valuable real estate on theintegrated circuit chip. To reduce the amount of real estate used, theresistor function can be provided with a transistor, such as byconnecting the drain of a metal-oxide-semiconductorfield-effect-transistor (MOSFET) to its gate. In some processes,providing a higher resistance value with a drain-to-gate connectedMOSFET is difficult.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram illustrating one example of a MOSFET.

FIG. 2 is a diagram illustrating one example of a ratioed logic circuitinverter.

FIG. 3 is a diagram illustrating one example of the layers in asemiconductor chip.

FIG. 4A is a cross-section diagram of a transistor taken along the lineA-A of FIG. 4B.

FIG. 4B is a top-view diagram illustrating one example of a transistor.

FIG. 5A is a cross-section diagram of a transistor taken along the lineB-B of FIG. 5B.

FIG. 5B is a top-view diagram illustrating one example of the transistorof FIG. 5A.

FIG. 6 is a top-view diagram illustrating one example of a transistorthat has a longer active channel length and a shorter inactive channellength.

FIG. 7A is a diagram illustrating one example of a substrate that has asource region, a drain region, and a channel.

FIG. 7B is a diagram illustrating one example of a gate disposed overthe channel.

FIG. 7C is a diagram illustrating one example of a second dielectriclayer disposed on the gate, drain region, and source region.

FIG. 7D is a diagram illustrating one example of an etched seconddielectric layer.

FIG. 7E is a diagram illustrating one example of metal 1 layer disposedon the second dielectric layer, gate, drain region, and source region.

FIG. 7F is a diagram illustrating one example of the transistor afteretching the metal 1 layer to form a gate lead, drain lead, and sourcelead.

DETAILED DESCRIPTION

In the following detailed description, reference is made to theaccompanying drawings which form a part hereof, and in which is shown byway of illustration specific embodiments in which the invention may bepracticed. In this regard, directional terminology, such as “top,”“bottom,” “front,” “back,” “leading,” “trailing,” etc., is used withreference to the orientation of the Figure(s) being described. Becausecomponents of embodiments of the present invention can be positioned ina number of different orientations, the directional terminology is usedfor purposes of illustration and is in no way limiting. It is to beunderstood that other embodiments may be utilized and structural orlogical changes may be made without departing from the scope of thepresent invention. The following detailed description, therefore, is notto be taken in a limiting sense, and the scope of the present inventionis defined by the appended claims.

FIG. 1 is a diagram illustrating one example of a MOSFET 20 thatincludes a semiconductor substrate 22 having a source 24, a drain 26,and a channel 28. The channel 28 is situated between source 24 and drain26, and a gate 30 is situated over channel 28. A layer of dielectricmaterial 32 is disposed between channel 28 and gate 30. Source 24includes an N+ doped region and drain 26 includes an N+ doped region.Channel 28 includes a p doped region situated between the N+ dopedregions of source 24 and drain 26.

In operation, a voltage is applied to gate 30 to create a conductivepath in channel 28 between drain 26 and source 24. With drain 26connected to a higher voltage and source 24 connected to a lowervoltage, such as ground, current flows from drain 26 to source 24. Alower voltage at gate 30 biases MOSFET 20 toward the off state, wherecurrent does not flow between drain 26 and source 24.

In ratioed logic circuits, a transistor such as MOSFET 20 can be used asa transistor or to provide the function of a resistor. To provide thefunction of a resistor, drain 26 is electrically coupled to gate 30. Ifa higher voltage is provided at drain 26 and gate 30 than at source 24,current flows from drain 26 to source 24.

FIG. 2 is a diagram illustrating one example of a ratioed logic circuitinverter 40 that includes a first transistor 42 and a second transistor44. Each of the first and second transistors 42 and 44 is similar toMOSFET 20. In another example, first transistor 42 is similar to MOSFET20 and second transistor 44 is a different type of transistor.

First transistor 42 functions as a resistive pull-up and secondtransistor 44 functions as a transistor pull-down. The drain D1 of firsttransistor 42 is electrically coupled to the gate G1 of first transistor42 and to VDD at 46. The source S1 of first transistor 42 iselectrically coupled to the drain D2 of second transistor 44 and tooutput OUT at 48. The gate G2 of second transistor 44 receives an inputvoltage VIN at 50 and the source S2 of second transistor 44 iselectrically coupled to a reference at 52, such as ground.

In operation, a low input voltage VIN at 50 biases second transistor 44off. First transistor 42 functions as a resistive pull-up to pull outputOUT at 48 to a high voltage value that approaches VDD. A high inputvoltage VIN at 50 biases second transistor 44 on, which pulls output OUTat 48 to a low output voltage. This low output voltage is substantiallyequal to VDD times the ratio of the on-resistance of second transistor44 to the summed resistances of first transistor 42 and theon-resistance of second transistor 44. First transistor 42 is built toprovide a resistance value that provides a low output voltage below thethreshold voltage of the next logic stage. Higher resistance valuesprovided by first transistor 42 result in lower output voltages andreduced power consumption. One way to provide higher resistance valuesvia first transistor 42 is to increase the channel length to width ratioof first transistor 42.

FIG. 3 is a diagram illustrating one example of the layers in asemiconductor chip 60. In one example, semiconductor chip 60 includestransistors, such as MOSFET 20 of FIG. 1. In one example, semiconductorchip 60 includes ratioed logic circuits, such as ratioed logic circuitinverter 40 of FIG. 2. In one example, semiconductor chip 60 is used inan inkjet printhead. In one example, semiconductor chip 60 is an inkjetcontrol chip.

Semiconductor chip 60 includes a semiconductor substrate 62, an oxidelayer 64, a polysilicon layer 66, a first dielectric layer 68, a metal 1layer 70, a second dielectric layer 72, and a metal 2 layer 74. Oxidelayer 64 is disposed on substrate 62 between substrate 62 andpolysilicon layer 66. First dielectric layer 68 is disposed onpolysilicon layer 66 and second dielectric layer 72 is disposed on metal1 layer 70 to separate metal 1 layer 70 from metal 2 layer 74. Metal 1layer 70 and metal 2 layer 74 provide gate, drain, and source leads andother connections in semiconductor chip 60. In one example, oxide layer64 is silicon dioxide (SiO2). In one example, second dielectric layer 72includes silicon nitride. In one example, second dielectric layer 72includes silicon carbide. In one example, second dielectric layer 72includes silicon nitride and silicon carbide.

FIGS. 4A and 4B are diagrams illustrating one example of a transistor 80that uses the layers of semiconductor chip 60 of FIG. 3.

FIG. 4A is a cross-section diagram of transistor 80 taken along the lineA-A of FIG. 4B. In one example, MOSFET 20 of FIG. 1 is similar totransistor 80. In one example, at least one of the first and secondtransistors 42 and 44 (shown in FIG. 2) is similar to transistor 80. Inone example, transistor 80 is used in an inkjet printhead system. Inother examples, transistor 80 is created using the layers of a differentprocess.

Transistor 80 includes substrate 62 that has N+ source regions 82 a and82 b, an N+ drain region 86, and a p channel 88 including p channelregions 88 a and 88 b. Drain region 86 includes a top surface 90, abottom 92, and sides 94 between top surface 90 and bottom 92. Channel88, including channel regions 88 a and 88 b, surrounds drain region 86around the sides 94 of drain region 86. Channel 88 is situated betweensource region 82 a and drain region 86 and between source region 82 band drain region 86. Source regions 82 a and 82 b are connected and partof one continuous source region 82 that surrounds channel 88.

Channel 88 includes a closed curve structure around drain region 86,where a curve is defined as an object similar to a line, but notrequired to be straight, which entails that a line is a special case ofa curve, namely a curve with null curvature. Also, a closed curve isdefined as a curve that joins up and has no endpoints. Channel 88,including channel regions 88 a and 88 b, is square. In one example,channel 88, including channel regions 88 a and 88 b, is rectangular andnot square. In one example, channel 88, including channel regions 88 aand 88 b, has at least one rounded interior or exterior corner.

A gate 100 is formed in polysilicon layer 66 and includes polysilicongate regions 66 a and 66 b situated over channel regions 88 a and 88 b,respectively. Dielectric layer 64 is situated between gate 100 andsubstrate 62. In one example, dielectric layer 64 is a silicon dioxidelayer. In one example, gate 100, including gate regions 66 a and 66 b,is the same shape as channel 88, including channel regions 88 a and 88b.

Dielectric layer 68 is disposed over gate 100, drain region 86, andsource region 82 including source regions 82 a and 82 b. A contact maskis used to create vias or holes in dielectric layer 68. The holes arecontact holes for gate region 66 b, drain region 86, and source region82 a. Metal 1 layer 70 is disposed on dielectric layer 68 and etched toform gate lead 102, drain lead 104, and source lead 106. Gate lead 102contacts gate region 66 b through the hole in dielectric layer 68, drainlead 104 contacts drain region 86 through the hole in dielectric layer68, and source lead 106 contacts source region 82 a through the hole indielectric layer 68.

Gate 100, including gate regions 66 a and 66 b, includes a closed curvestructure, where a curve is defined as an object similar to a line, butnot required to be straight, which entails that a line is a special caseof a curve, namely a curve with null curvature. Also, a closed curve isdefined as a curve that joins up and has no endpoints. In one example,gate 100, including gate regions 66 a and 66 b, is rectangular. In oneexample, gate 100, including gate regions 66 a and 66 b, is square. Inone example, gate 100, including gate regions 66 a and 66 b, has atleast one rounded interior or exterior corner. In operation, a voltageis applied to gate lead 102 and gate 100, including gate regions 66 aand 66 b, to create a conductive path in channel 88 between drain region86 and source regions 82 a and 82 b. The distance from drain region 86to source regions 82 is the channel length Lc. With drain lead 104 anddrain region 86 connected to a higher voltage and source lead 106 andsource regions 82 a and 82 b connected to a lower voltage, such asground, current flows from drain region 86 to source regions 82. A lowervoltage at gate lead 102 and gate 100 biases transistor 80 toward theoff state, where current does not flow between drain region 86 andsource regions 82.

To provide the function of a resistor, drain lead 104 and drain region86 are electrically coupled to gate lead 102 and gate 100. If a highervoltage is provided at drain lead 104 and gate lead 102 than at sourcelead 106, current flows from drain region 86 to source regions 82.

FIG. 4B is a top-view diagram illustrating the example of transistor 80.Some of the layers of transistor 80, such as dielectric layer 68, arenot shown for clarity in FIG. 4B. As described above, transistor 80includes gate 100, channel 88, drain region 86, and source region 82.Channel 88 is situated under gate 100 and indicated by dotted lines.Channel 88 surrounds drain region 86 and is situated between drainregion 86 and source region 82. Source region 82 surrounds channel 88.

Gate lead 102 is connected to gate 100 through dielectric layer 68 viacontact hole 110 (shown in dotted lines). Drain lead 104 is connected todrain region 86 through dielectric layer 68 via contact hole 112 (shownin dotted lines). Source lead 106 is connected to source region 82through dielectric layer 68 via contact hole 114 (shown in dottedlines).

Gate 100 is a square shaped closed curve structure, which is a specialcase of a rectangular shaped closed curve structure. Gate 100 includesfour sides and four right angle corners on each of the exterior side andthe interior side. Gate 100 has a gate length Lg that is the distancefrom exterior side 116 of gate 100 to interior side 118 of gate 100.Gate 100 has a gate width Wg that is the distance around gate 100 asmeasured at the midpoint between the interior and exterior sides of gate100. In one example, gate length Lg is the average gate length asmeasured at different points along the exterior and interior sides ofgate 100. In one example, gate length Lg is an equivalent gate lengththat is used in circuit simulations. In one example, gate width Wg isthe distance around gate 100 as measured at the exterior side of gate100. In one example, gate width Wg is the distance around gate 100 asmeasured at the interior side of gate 100. In one example, gate width Wgis an equivalent gate width that is used in circuit simulations. Inother examples, gate 100 can be another shape.

Channel 88 is also a square shaped closed curve structure, which is aspecial case of a rectangular shaped closed curve structure. Channel 88includes four sides and four right angle corners. Channel 88 has achannel length Lc that is the distance from exterior side 120 of channel88 to interior side 122 of channel 88. Channel 88 has a channel width Wcthat is the distance around channel 88 as measured at the midpointbetween the interior and exterior sides of channel 88, where channelwidth Wc is about the same as gate width Wg. In one example, channellength Lc is the average channel length as measured at different pointsalong the exterior and interior sides of channel 88. In one example,channel length Lc is an equivalent channel length that is used incircuit simulations. In one example, channel width Wc is the distancearound channel 88 as measured at the exterior side of channel 88. In oneexample, channel width Wc is the distance around channel 88 as measuredat the interior side of channel 88. In one example, channel width Wc isan equivalent channel width that is used in circuit simulations. Inother examples, channel 88 can be another shape.

Substantially all of channel 88 is an active channel region. The lengthto width ratio of the active channel region of channel 88 is equal tothe length to width ratio of channel 88, which is Lc/Wc.

The resistance value of a gate-to-drain connected transistor, such astransistor 80, may be too small for some applications, such as ratioedlogic circuits. One way to provide higher resistance values using atransistor is to increase the channel length to channel width ratio ofthe transistor. Increasing channel length Lc also increases the channelwidth Wc, which limits the increase in the channel length to width ratioto about a factor of 4.

FIGS. 5A and 5B are diagrams illustrating one example of a transistor200 that increases the resistance value of a gate-to-drain connectedtransistor by increasing the channel length to width ratio. Using themethod of transistor 200, the channel length to width ratio can beincreased beyond a factor of 4. Transistor 200 uses the layers ofsemiconductor chip 60 of FIG. 3.

FIG. 5A is a cross-section diagram of transistor 200 taken along theline B-B of FIG. 5B. In one example, MOSFET 20 of FIG. 1 is similar totransistor 200. In one example, at least one of the first and secondtransistors 42 and 44 (shown in FIG. 2) is similar to transistor 200. Inone example, transistor 200 is used in an inkjet printhead system. Inother examples, transistor 200 is created using the layers of adifferent process.

Transistor 200 includes substrate 62 that has N+ source regions 202 aand 202 b, an N+ drain region 206, and a p channel 208 including pchannel regions 208 a and 208 b. Drain region 206 includes a top surface210, a bottom 212, and sides 214 between top surface 210 and bottom 212.Channel 208, including channel regions 208 a and 208 b, surrounds drainregion 206 around the sides 214 of drain region 206. Channel 208 issituated between source region 202 a and drain region 206 and betweensource region 202 b and drain region 206. Source regions 202 a and 202 bare connected and part of one continuous source region 202 thatsurrounds channel 208.

Channel 208 includes a closed curve structure around drain region 206,where a curve is defined as an object similar to a line, but notrequired to be straight, which entails that a line is a special case ofa curve, namely a curve with null curvature. Also, a closed curve isdefined as a curve that joins up and has no endpoints. Channel 208,including channel regions 208 a and 208 b, is square. In one example,channel 208, including channel regions 208 a and 208 b, is rectangularand not square. In one example, channel 208, including channel regions208 a and 208 b, has at least one rounded interior or exterior corner.

A gate 216 (shown in FIG. 5B) is formed in polysilicon layer 66 over oneportion of channel 208. This one portion of channel 208 is referred toas active channel region 208 c (indicated with dotted lines under gate216). Gate 216 is not situated over the other portion of channel 208,which is referred to as the inactive channel region 208 d, whichincludes channel regions 208 a and 208 b. Dielectric layer 64 issituated between gate 216 and substrate 62 in the active channel region208 c and dielectric layer 64 is situated on substrate 62 in theinactive channel region 208 d. In one example, dielectric layer 64 is asilicon dioxide layer.

Dielectric layer 68 is situated over gate 216, drain region 206, andsource region 202 including source regions 202 a and 202 b. A contactmask is used to create vias or holes in dielectric layer 68. These holesare contact holes for gate 216, drain region 206, and source region 202a. Metal 1 layer 70 is disposed on dielectric layer 68 and etched toform gate lead 218, drain lead 220, and source lead 222. Gate lead 218contacts gate 216 through the hole in dielectric layer 68, drain lead220 contacts drain region 206 through the hole in dielectric layer 68,and source lead 222 contacts source region 202 a through the hole indielectric layer 68.

Gate 216 is a rectangular shaped gate having a gate length Lg and a gatewidth Wg. The active channel region 208 c under gate 216 has an activechannel length Lca and an active channel width Wca, where the gate widthWg and the active channel width Wca are substantially the same. In oneexample, gate 216 has at least one rounded interior or exterior corner.In other examples, gate 216 is another shape.

In operation, a voltage is applied to gate lead 218 and gate 216 tocreate a conductive path in active channel region 208 c between drainregion 206 and source region 202. The distance from drain region 206 tosource region 202 in the active channel region 208 c is the activechannel length Lca. With drain lead 220 and drain region 206 connectedto a higher voltage and source lead 222 and source region 202 connectedto a lower voltage, such as ground, current flows from drain region 206to source region 202. A lower voltage at gate lead 218 and gate 216biases transistor 200 toward the off state, where current does not flowbetween drain region 206 and source region 202.

To provide the function of a resistor, drain lead 220 and drain region206 are electrically coupled to gate lead 218 and gate 216. If a highervoltage is provided at drain lead 220 and gate lead 218 than at sourcelead 222, current flows from drain region 206 to source region 202. Inanother example, to provide the function of a resistor, drain lead 220and drain region 206 can be electrically coupled to a high voltage, suchas VDD, and gate lead 218 and gate 216 can be electrically coupled to acontrol output from a previous stage, which can be set to a highvoltage.

FIG. 5B is a top-view diagram illustrating the example of transistor200. Some of the layers of transistor 200, such as dielectric layer 68,are not shown for clarity in FIG. 5B. As described above, transistor 200includes gate 216, channel 208, drain region 206, and source region 202.Active channel region 208 c is situated under gate 216 and indicated bydotted lines. Channel 208 surrounds drain region 206 and is situatedbetween drain region 206 and source region 202. Source region 202surrounds channel 208.

Gate lead 218 is connected to gate 216 through dielectric layer 68 viacontact hole 224 (shown in dotted lines). Drain lead 220 is connected todrain region 206 through dielectric layer 68 via contact hole 226 (shownin dotted lines). Source lead 222 is connected to source region 202through dielectric layer 68 via contact hole 228 (shown in dottedlines).

Gate 216 is a rectangular shaped gate having four sides and four rightangle corners. Gate 216 has a gate length Lg that is the distance fromone side 230 to the other side 232. Gate 216 has a gate width Wg that isthe distance from one side 234 to the other side 236. In one example,gate length Lg is the average gate length as measured at differentpoints along the sides of gate 216 that are next to drain 206 and source202. In one example, gate length Lg is an equivalent gate length that isused in circuit simulations. In other examples, gate 216 can be anothershape.

Channel 208 includes active channel region 208 c and inactive channelregion 208 d. Active channel region 208 c is a rectangular shapedchannel having four sides and four right angle corners under gate 216.Active channel region 208 c has an active channel length Lca that is thedistance from one side 238 to the other side 240. Active channel region208 c has an active channel width Wca that is the distance from one side234 to the other side 236, where the gate width Wg and the activechannel width Wca are substantially the same. In one example, activechannel length Lca is the average channel length as measured atdifferent points along the sides of active channel region 208 c, whichare next to drain 206 and source 202. In one example, active channellength Lca is an equivalent channel length that is used in circuitsimulations. In other examples, active channel region 208 c can beanother shape.

Channel 208, including active channel region 208 c and inactive channelregion 208 d, has a channel length Lc that is the distance from drain206 to source 202. Channel 208, including active channel region 208 cand inactive channel region 208 d, has a channel width Wc that is thedistance around channel 208 as measured at the midpoint between theinterior and exterior sides of channel 208. In one example, channellength Lc is the average channel length as measured at different pointsalong the drain 206 and source 202. In one example, channel length Lc isan equivalent channel length that is used in circuit simulations. In oneexample, channel width Wc is the distance around channel 208 as measuredat the exterior side of channel 208. In one example, channel width Wc isthe distance around channel 208 as measured at the interior side ofchannel 208. In one example, channel width Wc is an equivalent channelwidth that is used in circuit simulations.

In transistor 200, the active channel length Lca is substantially equalto the channel length Lc, and the active channel width Wca is less thanthe channel width Wc. Thus, the active channel length to width ratioLca/Wca is greater than the channel length to width ratio Lc/Wc.

Transistor 200 includes drain 206 surrounded by channel 208 to isolatedrain 206 in a process that does not include field oxide. Gate 216increases the gate length to width ratio and the active channel lengthto width ratio, which increases the resistance value of a gate-to-drainconnected transistor 200. Using this methodology, the active channellength to width ratio can be increased beyond a factor of 4. To reducethe amount of real estate used on a semiconductor chip, the activechannel length Lca can be increased, while providing a minimum sizedchannel length in the inactive channel region 208 d.

FIG. 6 is a top-view diagram illustrating one example of a transistor300 that has a longer active channel length Lca and a shorter inactivechannel length Lci. The longer active channel length Lca increases theactive channel length to width ratio Lca/Wca, which increases theresistance value of a gate-to-drain connected transistor. The shorterinactive channel length Lci reduces the amount of real estate used bytransistor 300 on a semiconductor chip. Using this methodology, theactive channel length to width ratio can be increased to provide ahigher resistance value and the transistor profile can be minimized toreduce size. Transistor 300 is manufactured using the process depictedin FIG. 3, including the layers of semiconductor chip 60 of FIG. 3. Someof these layers, such as dielectric layer 68, are not shown for clarityin FIG. 6. Transistor 300 is similar to transistor 200.

Transistor 300 includes gate 302, channel 304, drain region 306, andsource region 308. Active channel region 304 a is situated under gate302 and indicated by dotted lines. Channel 304 surrounds drain region306 and is situated between drain region 306 and source region 308.Source region 308 surrounds channel 304.

Gate lead 310 is connected to gate 302 through dielectric layer 68 viacontact hole 312 (shown in dotted lines). Drain lead 314 is connected todrain region 306 through dielectric layer 68 via contact hole 316 (shownin dotted lines). Source lead 318 is connected to source region 308through dielectric layer 68 via contact hole 320 (shown in dottedlines).

Gate 302 is a rectangular shaped gate having four sides and four rightangle corners. Gate 302 has a gate length Lg that is the distance fromone side 322 to the other side 324. Gate 302 has a gate width Wg that isthe distance from one side 326 to the other side 328. In one example,gate length Lg is the average gate length as measured at differentpoints along the sides of gate 302, which are next to drain 306 andsource 308. In one example, gate length Lg is an equivalent gate lengththat is used in circuit simulations. In other examples, gate 302 can beanother shape.

Channel 304 includes active channel region 304 a and inactive channelregion 304 b. Active channel region 304 a is a rectangular shapedchannel having four sides and four right angle corners under gate 302.Active channel region 304 a has an active channel length Lca that is thedistance from one side 330 to the other side 332. Active channel region304 a has an active channel width Wca that is the distance from one side326 to the other side 328, where the gate width Wg and the activechannel width Wca are substantially the same. In one example, activechannel length Lca is the average channel length as measured atdifferent points along the sides of active channel region 304 a, whichare next to drain 306 and source 308. In one example, active channellength Lca is an equivalent channel length that is used in circuitsimulations. In other examples, active channel region 304 a can beanother shape.

Inactive channel region 304 b has an inactive channel length Lci that isthe distance from drain region 306 to an exterior side of inactivechannel region 304 b. Inactive channel length Lci is shorter than activechannel length Lca to reduce the size of transistor 300 and use lessreal estate on the semiconductor chip. Active channel length Lca islonger than inactive channel length Lci to increase the active channellength to width ratio Lca/Wca, which increases the resistance value of agate-to-drain connected transistor 300.

Channel 304, including active channel region 304 a and inactive channelregion 304 b, has a channel width Wc that is the distance around channel304 as measured at the midpoint between the interior and exterior sidesof channel 304. Channel 304, including active channel region 304 a andinactive channel region 304 b, has a channel length Lc that correspondsto the distance from drain 306 to source 308 and the active channellength Lca and the inactive channel length Lci. In one example, thechannel length Lc is equal to (Lca+3Lci)/4. In one example, channellength Lc is the average channel length as measured at different pointsalong the drain 206 and source 202. In one example, channel length Lc isan equivalent channel length that is used in circuit simulations. In oneexample, channel width Wc is the distance around channel 304 as measuredat the exterior side of channel 304. In one example, channel width Wc isthe distance around channel 304 as measured at the interior side ofchannel 304. In one example, channel width Wc is an equivalent channelwidth that is used in circuit simulations.

In transistor 300, the active channel length Lca is greater than thechannel length Lc, and the active channel width Wca is less than thechannel width Wc. Thus, the active channel length to width ratio Lca/Wcais greater than the channel length to width ratio Lc/Wc.

Transistor 300 includes drain 306 surrounded by channel 304 to isolatedrain 306 in a process that does not include field oxide. Gate 302increases the gate length to width ratio and the active channel lengthto width ratio, which increases the resistance value of a gate-to-drainconnected transistor 300. Using this methodology, the active channellength to width ratio can be increased and the amount of real estateused on a semiconductor chip minimized.

FIGS. 7A-7F are diagrams illustrating one example of a method ofmanufacturing a transistor 400. Transistor 400 is similar to transistor200 of FIGS. 5A and 5B and transistor 300 of FIG. 6.

FIG. 7A is a diagram illustrating one example of a substrate 402 thathas N+ source regions 404 a and 404 b, an N+ drain region 406, and a pchannel 408 including p channel regions 408 a and 408 b. Drain region406 includes a top surface 410, a bottom 412, and sides 414 between topsurface 410 and bottom 412. Channel 408, including channel regions 408 aand 408 b, surrounds drain region 406 around the sides 414 of drainregion 406. Channel 408 is situated between source region 404 a anddrain region 406 and between source region 404 b and drain region 406.Source regions 404 a and 404 b are connected and part of one continuoussource region 404 that surrounds channel 408.

Channel 408 includes a closed curve structure around drain region 406,where a curve is defined as an object similar to a line, but notrequired to be straight, which entails that a line is a special case ofa curve, namely a curve with null curvature. Also, a closed curve isdefined as a curve that joins up and has no endpoints. In one example,channel 408 surrounds drain region 406 with a uniform channel length Lc.In one example, channel 408 surrounds drain region 406 with anon-uniform channel length Lc. In one example, channel 408, includingchannel regions 408 a and 408 b, is square. In one example, channel 408,including channel regions 408 a and 408 b, is rectangular and notsquare. In one example, channel 408, including channel regions 408 a and408 b, has at least one rounded interior or exterior corner.

FIG. 7B is a diagram illustrating one example of a gate 416 disposedover channel 408. Dielectric layer 64 is disposed on substrate 402 andpolysilicon layer 66 is disposed on dielectric layer 64. Dielectriclayer 64 is patterned to remain on channel 408 and includes dielectriclayer 64 a on channel region 408 a and dielectric layer 64 b on channelregion 408 b. Gate 416 is formed in polysilicon layer 66 and includespolysilicon gate regions 66 a and 66 b situated over channel regions 408a and 408 b, respectively. Dielectric layer 64 is situated between gate416 and substrate 402. In one example, dielectric layer 64 is a silicondioxide layer. In one example, gate 416 is the same shape as channel408.

FIG. 7C is a diagram illustrating one example of a second dielectriclayer 68 disposed on gate 416, drain region 406, and source region 404,including source regions 404 a and 404 b.

FIG. 7D is a diagram illustrating one example of etched dielectric layer68, after etching dielectric layer 68 via a contact mask to create holesin dielectric layer 68. Contact holes are etched in dielectric layer 68to make contact to gate 416, drain region 406, and source region 404 a.The contact hole for gate 416 is etched through dielectric layer 68 overactive channel regions, such as active channel region 208 c intransistor 200 and active channel region 304 a in transistor 300.Dielectric layer 68 is also etched away via the contact mask overportions of gate 416 that are over inactive channel regions, includingchannel regions 408 a and 408 b, and inactive channel regions such asinactive channel region 208 d in transistor 200 and inactive channelregion 304 b in transistor 300.

FIG. 7E is a diagram illustrating one example of metal 1 layer 70disposed on dielectric layer 68, gate 416, drain region 406, and sourceregion 404. Metal 1 layer 70 contacts gate 416 through the gate contacthole and over the inactive channel region. Metal 1 layer 70 contactsdrain region 406 through the drain contact hole and source region 404through the source contact hole over source region 404 a.

FIG. 7F is a diagram illustrating one example of transistor 400 afteretching metal 1 layer 70 to form a gate lead (not shown), drain lead418, and source lead 420. Metal 1 layer 70 is etched away in areas thatare unprotected in the photolithographic process, including over theactive channel region, down to dielectric layer 68. Metal 1 layer andgate 416 are etched away over the inactive channel region down todielectric layer 64, including dielectric layers 64 a and 64 b.

The gate lead contacts gate 416 through the contact hole in dielectriclayer 68 over the active channel region of transistor 400. Drain lead418 contacts drain region 406 through the contact hole in dielectriclayer 68, and source lead 420 contacts source region 404 through thecontact hole in dielectric layer 68 over source region 404 a.

Etching away metal 1 layer 70 and a portion of gate 416 creates theactive channel region and the inactive channel region in transistor 400,where the active channel region has an active channel region length towidth ratio that is greater than the channel length to width ratio oftransistor 400 prior to etching away metal 1 layer 70 and a portion ofgate 416. In one example, etching away metal 1 layer 70 and a portion ofgate 416 creates an active channel region and an inactive channelregion, which provides a longer channel length in the active channelregion and a shorter channel length in the inactive channel region.

Transistor 400 includes drain 406 surrounded by channel 408 to isolatedrain 406 in a process that does not include field oxide. Gate 416 isetched to increase the gate length to width ratio and the active channellength to width ratio, which increases the resistance value of agate-to-drain connected transistor 400. Using this methodology, theactive channel length to width ratio can be increased and the amount ofreal estate used on a semiconductor chip minimized.

Although specific embodiments have been illustrated and describedherein, it will be appreciated by those of ordinary skill in the artthat a variety of alternate and/or equivalent implementations may besubstituted for the specific embodiments shown and described withoutdeparting from the scope of the present invention. This application isintended to cover any adaptations or variations of the specificembodiments discussed herein. Therefore, it is intended that thisinvention be limited only by the claims and the equivalents thereof.

1. A transistor comprising: a substrate; a drain in the substrate; asource in the substrate; a channel between the drain and the source, thechannel surrounding the drain and having a channel length to widthratio; and a gate over the channel to provide an active channel regionthat has an active channel region length to width ratio that is greaterthan the channel length to width ratio.
 2. The transistor of claim 1,wherein the gate comprises polysilicon.
 3. The transistor of claim 1,wherein the channel comprises a plurality of channel regions, and thegate comprises a plurality of gate regions over respective channelregions of the plurality of channel regions.
 4. The transistor of claim3, further comprising a gate lead electrically contacted to the gateregions, a drain lead electrically contacted to the drain, and a sourcelead electrically contacted to the source, the gate lead, the drainlead, and the source lead formed by a first metal layer.
 5. Thetransistor of claim 1, wherein the gate is disposed over a first portionof the channel, and is not disposed over a second portion of thechannel, wherein the active channel region is provided by the firstportion, and the inactive channel region is provided by the secondportion.
 6. The transistor of claim 5, further comprising a dielectriclayer between the gate and the first portion of the channel.
 7. Thetransistor of claim 5, wherein a width of the active channel region isless than a width of the channel.
 8. The transistor of claim 7, whereinthe width of the active channel region is defined by a width of thegate.
 9. The transistor of claim 1, wherein the channel is a closedcurve structure around the drain.
 10. The transistor of claim 1, whereinthe channel has a uniform channel length around the drain.
 11. Thetransistor of claim 1, wherein the channel has a non-uniform channellength around the drain.
 12. The transistor of claim 1, wherein thechannel includes an inactive channel region, and the channel has alonger channel length in the active channel region and a shorter channellength in the inactive channel region.
 13. The transistor of claim 1,wherein the source surrounds the channel.
 14. A semiconductor devicecomprising: a substrate; a drain in the substrate; a source in thesubstrate; a channel between the drain and the source, the channelsurrounding the drain and having an active channel region that has anactive channel region length, and an inactive channel region that has aninactive channel region length that is less than the active channelregion length; and a gate disposed over the active channel region. 15.The semiconductor device of claim 14, wherein the gate is not disposedover the inactive channel region of the channel.
 16. The semiconductordevice of claim 14, wherein the gate comprises polysilicon.
 17. Thesemiconductor device of claim 14, further comprising: a gate leadelectrically contacted to the gate regions, a drain lead electricallycontacted to the drain, and a source lead electrically contacted to thesource, the gate lead, the drain lead, and the source lead formed by afirst metal layer.
 18. The semiconductor device of claim 14, wherein thesubstrate, the drain, the source, the channel, and the gate are part ofa first transistor, the semiconductor device further comprising a secondtransistor comprising: a substrate; a drain in the substrate of thesecond transistor; a source in the substrate of the second transistor; achannel between the drain of the second transistor and the source of thesecond transistor, the channel of the second transistor having an activechannel region, wherein a length to width ratio of the active channelregion of the channel of the second transistor is equal to a length towidth ratio of the channel of the second transistor.
 19. Thesemiconductor device of claim 18, wherein a resistance of the firsttransistor is greater than a resistance of the second transistor. 20.The semiconductor device of claim 19, wherein the source of the firsttransistor is electrically connected to the drain of the secondtransistor.